This application relates to an apparatus for the implantation and extraction of osteal prostheses employing an ultrasonic energy source and designed for use by orthopedic surgeons.
A variety of techniques and apparatus for implanting and removing orthopedic prostheses have been developed since replacement parts for hip joints and like were first used well over half a century ago. In particular, total joint replacements have been carried out in a large number of patients for some time. While some improvements have been made both in the techniques for implanting the prosthetic devices and in the prostheses themselves, a need remains for improved surgical procedures which are less time consuming and minimize trauma to the patient.
Revision total hip arthroplasty for replacement of defective or damaged prostheses has in particular taken on increasing importance, as the number of patients requiring such revisions increases dramatically. The procedures currently employed often result in complications, many of which are related to removal of the femoral prosthesis and the intramedullary cement mantle. The increased operating time required for revisions is associated with increased blood loss, a higher infection rate and increased postoperative morbidity. Femora perforation during cement removal, with the possibility of intraoperative or postoperative femoral fracture, is a well-known and particularly serious complication.
None of the previously available procedures for removal of the femoral prosthesis and cement mantle is entirely satisfactory. For example, while high speed cutting tools (such as the Midas Rex and Anspach pneumatic tools) have been found effective in cement removal, the use thereof may be hazardous due to the fact that the femoral cortex is easily perforated. Image intensification may reduce the risk of perforation somewhat, but is time-consuming and adds the additional risk of excessive radiation exposure. The alternative technique of controlled femoral perforation requires wide soft tissue exposure and creates multiple potential stress risers; as it has been argued that any cortical defect (including such deliberately induced perforations) could increase the chances of intraoperative or postoperative fracture, such procedure is clearly not without a potentially significant risk of serious injury to the patient.
In an effort to provide improved procedures for the removal of the femoral cement mantle, various new techniques have been developed. For example, a CO.sub.2 laser has been employed for cement removal. In this context, use of a laser has been found to have some significant disadvantages. The instrumentation required is cumbersome; moreover, vaporization of the cement is slow, the fumes toxic and flammable, and the potential for thermal necrosis of endosteal bone significant. Similarly, the lithiotriptor was explored as a potential tool for fracturing the cement mantle. It was determined, however, that the shock wave is difficult to focus, and thus microfractures of adjacent cortical bone occur frequently.
Systems using ultrasonic generators in conjunction with transducer or horn elements have heretofore been developed for use in specific medical applications. A variety of ultrasonic tools are currently employed almost routinely by practitioners in a number of fields, including neurosurgery, ophthalmology and dentistry. As these devices are tailored for use in particular surgical applications, they are found to have little if any applicability outside the particular context for which they were designed.
Several systems have heretofore been developed for use in ophthalmic cataract removal, and phacoemulsification has become standard practice for removal of cataracts. In addition, "CUSA" (cavitation ultrasonic aspirator) systems have gained some currency among surgeons involved in neurological tissue resections. Ultrasonic equipment is also in current use for scaling (removal) of calcified plaque from teeth and for tissue emulsification and homogenization. All of the above-described devices are of limited applicability outside the particular context for which they were designed.
Ultrasonic devices have been employed for a variety of different applications outside the medical field as well. For example, ultrasonic apparatus has particular utility in the welding of plastics. Such equipment would also clearly be unsuitable for use in the context of surgery, where delicate living tissue must be carefully manipulated under sterile conditions.
U.S. Pat. No. 4,248,232 (Engelbrecht et al.) suggests the use of an osteotome for removal of osteal prostheses. This patent, however, is completely silent with respect to the type of osteotome which would be suitable for use in such a context. Moreover, the patent fails to indicate any parameters whatsoever for the use of an osteotome in orthopedic surgery. Therefore, it is not surprising that there has been no reported use of ultrasonic devices in the context of orthopedic surgery to date in the medical literature. In fact, since the issuance of U.S. Pat. No. 4,248,232 there has been a continued search for alternative techniques to solve the long-standing problems encountered in the removal of damaged prostheses, as well as in the implantation of new prosthetic devices. Accordingly, there remains a need for apparatus that would enable rapid and atraumatic removal of a prosthesis and/or the cement mantle surrounding same, as well as the safe and efficient implantation of prostheses.